1. Field of the Invention
The invention relates to a process for preparing 1-olefins by telomerization of compounds having conjugated double bonds with a telogen in the presence of a noble metal telomerization catalyst, hydrogenation of the telomer and cleavage of the hydrogenated intermediate.
2. Description of the Background
1-Olefins such as 1-octene are used in large quantities in the production of various chemical products. For example, surface-active substance, plasticizers, lubricants and polymers are produced from 1-octene. Another large application is its use as comonomer in polymers, in particular in polyethylene.
Virtually all processes used commercially at the present time for producing 1-octene are based on the raw material ethene. Ethene is oligomerized to give a product spectrum of α-olefins as main products. With appropriate choice of catalyst and process conditions, the amount of 1-octene in the product can be optimized and is then about 25%. Apart from these processes by means of which the major part of the 1-octene produced is obtained, the isolation of 1-octene from the product mixture from the Fischer-Tropsch reaction has attained some importance.
Apart from the ethene-based processes, processes which use 1,3-butadiene as raw material for preparing 1-octene are also known from the literature. However, 1-octene is not obtainable directly from butadiene, for example by means of dimerization, but is obtained after a plurality of process steps. Thus, the patent application WO 92/10450 describes a process in which 1,3-butadiene is reacted preferably with methanol or ethanol to form a 2,7-octadienyl ether which is then hydrogenated to the octyl ether and is then cleaved to give 1-octene. EP-A-0 440 995 follows an analogous route, but the reaction in the first step is with a carboxylic acid. The first process step, which is generally referred to as telomerization, is involved in both the processes. In telomerization, a telogen (in EP-A-0 440 995 the carboxylic acid) is generally reacted with a taxogen (1,3-butadiene, 2 equivalents) to form a telomer.
Examples of telomerization reactions are described, inter alia, in E. J. Smutny, J. Am. Chem. Soc. 1967, 89, 6793; S. Takahashi, T. Shibano, N. Hagihara, Tetrahedron Lett. 1967, 2451; EP-A-0 561 779, U.S. Pat. Nos. 3,499,042, 3,530,187, GB 1 178 812, NL 6 816 008, GB 1 248 593, U.S. Pat. Nos. 3,670,029, 3,670,032, 3,769,352, 3,887,627, GB 1 354 507, DE 20 40 708, U.S. Pat. Nos. 4,142,060, 4,146,738, 4,196,135, GB 1, 535 718, U.S. Pat. No. 4,104,471, DE 21 61 750 and EP-A-0 218 100.
In the known processes for preparing 1-octene on the basis of butadiene, as described, for example, in WO 92/10450 or EP-A-0 440 995, the 1-octene is obtained by cleavage of an n-octane substituted in the 1 position. The selectivities in this step are often unsatisfactory. Thus, WO 92/10450 reports a selectivity to octenes of 66% at a conversion of 80% in the cleavage of 1-methoxyoctane.
Catalysts which have been found to be effective for telomerization are halogen-free palladium(0) and palladium(II) compounds (A. Behr, in “Aspects of Homogeneous Catalysis”; editor R. Ugo, D. Reidel Publishing Company, Doordrecht/Boston/Lancaster, 1984, Vol. 5, 3). In addition, compounds of other transition metals such as cobalt (R. Baker, A. Onions, R. J. Popplestone, T. N. Smith, J. Chem. Soc., Perkin Trans. II 1975, 1133-1138), rhodium, nickel (R. Baker, D. E. Halliday, T. N. Smith, J. Organomet. Chem. 1972, 35, C61-C63; R. Baker, Chem. Rev. 1973, 73, 487-530; R. Baker, A. H. Cook, T. N. Smith, J. Chem. Soc., Perkin Trans. II 1974, 1517-1524) and platinum have also been used as catalysts. However, the latter systems are inferior to palladium complexes in terms of activity and selectivity.
WO 91/09822 describes a continuous process using palladium acetylacetonate/2 equivalents of triphenylphosphine as catalyst. Catalyst productivities (turnover numbers) of up to 44,000 are achieved here. However, the chemoselectivities to the target product at such catalyst turnover numbers are <85%. The use of palladium complexes or palladium salts in combination with carboxylic acids for the telomerization of butadiene is known from EP 0 440 995. However, the complexing agent is not specified.
A process for the preparation of octadienyl ethers was described in 1987 by National Distillers and Chem. Corp. (U.S. Pat. Nos. 4,642,392, 4,831,183). The product mixture was separated from the catalyst (palladium acetate/5 equivalents of triphenylphosphine) by distillation, leaving the catalyst as a solution in a high-boiling solvent. The catalyst can be reused up to twelve times when supplementary phosphine is added each time. However, the initial batch (Example 1) gave the linear ether in a yield of only 57% (corresponding to a TON of 2000). The n/iso ratio of the telomers is in this case only 3.7:1. In U.S. Pat. No. 4,831,183, the mixture was separated from the reaction solution by, for example, extraction with hexane. The telomerization was carried out in dimethylformamide or sulfolane using the catalyst mixture palladium(II) acetate/3 equivalents of triphenylphosphinemonosulfonate. Longer-chain primary alcohols such as ethanol, propanol and butanol (J. Beger, H. Reichel, J. Prakt. Chem. 1973, 315, 1067) also form the corresponding telomers with butadiene. However, the catalytic activity of the known catalysts is even lower here than in the abovementioned cases. Thus, under identical reaction conditions [Pd(acetylacetonate)2/PPh3/butadiene/alcohol =1:2:2000:5000; 60° C./10 h], the telomers of methanol are formed in a yield of 88%, those of propanol are formed in a yield of 65% and those of nonanol are formed in a yield of only 28%.
Like alcohols, carboxylic acids are suitable nucleophiles in telomerization reactions. Acetic acid and butadiene give the corresponding octadienyl derivatives in good yields (DE 2 137 291). The ratio of linear and branched products (n/iso ratio) can be influenced via the ligands on the palladium (D. Rose, H. Lepper, J. Organomet . Chem. 1973, 49, 473). A ratio of 4/1 was achieved using triphenylphosphine as ligand, and the ratio could be increased to 17/1 when using tris(o-methylphenyl) phosphite. Other carboxylic acids such as pivalic acid, benzoic acid and methacrylic acid, and also dicarboxylic acids, can likewise be reacted with butadiene.
Shell Oil has described a process for preparing α-olefins based on the telomerization of conjugated dienes with carboxylic acids in U.S. Pat. No. 5,030,792.
Telomerization reactions in which water is used as nucleophiles have been intensively studied by, inter alia, the Kuraray company (U.S. Pat. Nos. 4,334,117, 4,356,333, 5,057,631). In these reactions, phosphines, usually water-soluble phosphines, or phosphonium salts (EP 0 296 550) are used as ligands. The use of water-soluble disphosphines as ligands is described in WO 98/08794. DE 195 23 335 discloses the reaction of alkadienes with water in the presence of phosphonite or phosphinite ligands.
GB 1 535 718 describes the telomerization of butadiene with amines, catalyzed by palladium(0) complexes. EP 939074 and EP 773211 describes the preparation of octa-2,7-diethyl-1-amine by telomerization of ammonia and butadiene.
The telomerization of butadiene with nucleophiles such as formaldehyde, aldehydes, ketones, carbon dioxide, sulfur dioxide, sulfinic acids, β-keto esters, β-diketones, malonic esters, α-formyl ketones and silanes is likewise described in the literature.
In summary, it can be said that the known palladium-phosphine catalysts do not give satisfactory catalytic turnover numbers (TONs, catalyst productivities) in telomerization reactions of butadienes with alcohols. Industrially desired productivities of >100,000 have rarely been described for known systems. At the same time, high chemoselectivities and regioselectivities of >95% should be achieved in order to obtain an ecologically advantageous process.